Various types of marking pens have been produced which are designed to apply ink or other liquid material to a receptive surface, e.g. paper.
The pen assembly of this invention is completely stable during prolonged periods of storage, yet contains a full complement of coloring material, whereas ordinary porous nibbed pens of the prior art are subject to leakage, drying out, clogging and similar difficulties in storage.
My pen may be made operable by the introduction of solvent (e.g. water) only, whereas many prior art porous nibbed pens (and those on sale that I have encountered) have commonly contained or required the addition of liquid ink.
In the preferred embodiments of my pen, water (or solvent) is introduced in controlled amounts by means of a self-measuring porous plug, so that the desired tint is conveniently and uniformly attainable. This accomplishment is not available in prior art porous nibbed pens with which I am familiar. My pen assembly makes it possible to obtain sufficient solution of the dye and diffusion of the ink throughout the assembly of the porous plug or body and the nib, so that the pen can be used within a short time, e.g. 2 to 10 minutes, after insertion of the wet porous body or plug into the barrel of my pen. U.S. Pat. No. 3,003,182 provides a porous reservoir body filled with liquid ink and from which the ink flows by capillarity to an easily removable and replaceable porous felt writing tip or nib. Ink is introduced by removing the reservoir body and dipping it in liquid ink, with attendant likelihood of soiling the fingers. Interchangeability of nibs is achieved in part by minimal contact between nib and reservoir, thereby impeding the flow of ink to the writing tip.
In the device of U.S. Pat. No. 3,481,677 the nib and reservoir are combined in a single expandable porous body which may contain a soluble dye. Dipping the writing tip in an appropriate aqueous dye solution results in expansion of the porous body so that a pointed writing tip cannot be maintained.
In U.S. Pat. No. 3,544,229 there is described a marking pen having an ink-conducting point or nib extending into an ink-containing chamber wherein the liquid ink is capillarily retained by a loose mass of threads formed of loosely twisted fibers. The construction requires that the ink be added after the fibrous mass is in place, an operation requiring considerable skill.